1. Field of the Invention
This invention relates to an image reading apparatus for placing a book or a bound document that is turned upward for reading an image of the leaf surface of the book or the bound document.
2. Description of the Related Art
In the conventional field of image reading apparatuses, the technique, which is composed of detecting a shaded zone generated by the protrusion of the central bound part in the leaf surface (the surface of spread pages of abound document) in terms of the shade depth of an image itself in the bound part and eliminating the detected zone during the reading of the bound document, has been proposed as disclosed in Japanese Laid-Open Patent Applications JP-A-62-14664, JP-A-63-249869, and JP-A-03-79158, for example. By this technique, it is avoided that the shade and shadow of the bound part, which does not need to be read out as an image, are generated in the center of the leaf surface and the image being read out of a bound document is obscured.
In the method of detecting the bound part and eliminating the detected zone as used in the conventional image reading apparatus, it is, however, incurred that particularly when the bound document is placed aslant, the shade and shadow of the bound part in the center of the leaf surface and the image information such as characters and ruled lines confusedly exist within data on the same main-scanning line (for example, in the longitudinal direction of the apparatus). Such a situation gives rise to the drawback that the bound part is not easily detected and the elimination of the center line zone is not properly attained.